A species' successful invasion into a new site depends on its ability to persist in the local environment. An experiment was conducted to examine the response of giant reed to intermittent periods of shading for 2 yr. Results indicate that giant reed persisted when exposed to significant shading (i.e., 90% reduction of full sun) and that shading also caused changes in a number of plant characteristics, such as stem height, internode length, leaf nitrogen, leaf chlorophyll content, specific leaf area, total leaf area per plant, and leaf life span. Estimates of leaf photosynthetic rates did not differ across shade levels. Giant reed's ability to persist and grow under intermittent low-light conditions implies that plants would be poised to take advantage of sun flecks and disturbances that create gaps within the resident plant community.

Four rates of aminopyralid (30, 60, 90, and 120 g ae ha−1 [0.4, 0.9, 1.3, and 1.8 oz ae acre−1]) were compared for their ability to reduce abundance of nonnative dicot species and favor native species in an invaded Cascade Mountain meadow near Trout Lake, WA. Treatments were applied in two replicated studies (June 2009 and 2010), and foliar cover and species richness were monitored for two years. First-year control of nonnative dicots from application of 30 g ae ha−1 of aminopyralid (69%) was greater than that of native dicots (29%); whereas, significant control of both species groups occurred at the higher rates. By the second year after treatment, absolute differences in cover between treated and non-treated plots averaged −17% and −21% for native and nonnative dicots, respectively, and +1% and +27% for native and nonnative monocots, respectively. First-year control of Canada thistle and oxeye daisy was greater after treatment in 2009 (88% and 90%, respectively) than after treatment in 2010 (56% and 55%, respectively), probably because lower spring temperatures in 2010 limited vegetation development and plant susceptibility to aminopyralid. Cover of Kentucky bluegrass and sheep fescue averaged 20% and 6% greater, respectively, in treated plots than in non-treated plots. Application of 30 g ae ha−1 of aminopyralid had no detectable effect on second-year richness of native and nonnative species relative to non-treated plots; however, higher rates caused 24% to 43% reductions in richness of each species group. Research results suggest that application of aminopyralid at 30 g ae ha−1 has the potential to reduce abundance of nonnative dicot species in similar meadow communities of the Pacific Northwest with little or no negative impacts to abundance and richness of native species. As a potential strategy to limit the subsequent spread of Kentucky bluegrass, a grass herbicide, such as fluazifop or sethoxydim, could be added to the treatment.

The Appalachian region of the United States is home to the largest temperate deciduous forest in the world, though surface mining has caused significant forest loss. Many former coal mines are now dominated by invasive plants, which often inhibit establishment of desirable species, especially slower-growing native trees. Autumn-olive (Elaeagnus umbellata Thunb.) is a nonnative, nitrogen-fixing shrub that was historically planted on former coalfields, but now impedes reclamation. To better understand the influence of E. umbellata management practices on hardwood establishment, we evaluated two common management practices: cutting and cut stump herbicide treatment. Planted native tree species, including black cherry (Prunus serotina Ehrh.), pin oak (Quercus palustris Münchh.), and red maple (Acer rubrum L.), were monitored for survival and performance over two growing seasons following E. umbellata removal. In each plot, we also measured plant-available nitrate (NO3−) and ammonium (NH4+) in soils using ionic exchange membranes. At the end of the first growing season, native tree survival was high, and the presence or absence of E. umbellata had little effect on tree survival or growth, despite the higher plant-available nitrate where E. umbellata was present. By the end of the second growing season, native tree survival dropped to 20% to 60% and varied among E. umbellata treatments. Survival was highest when E. umbellata was cut and treated with herbicide, though tree growth was similar across all treatments without E. umbellata. When establishing native trees to replace E. umbellata, cutting and herbicide application treatment of the invader resulted in the highest overall efficacy (100% control), though the most cost-effective method may be to simply cut mature stands despite regrowth, as this resulted in equivalent native tree growth over 2 yr. While this allowed E. umbellata regeneration, it provided sufficient invader control to allow initial tree establishment. Cutting and herbicide application treatment resulted in less E. umbellata regeneration and appears to provide greater assurance that established trees will persist over the long term.

The composition of nonnative floras is influenced by a region’s socioeconomic history, yet rarely are these factors studied alongside plant naturalization rates over time. Such information is especially critical for archipelagos, which often host large numbers of nonnative plants and would benefit from prevention of inter-island spread. We compiled the first record of occurrence and first record of naturalization for all naturalized plants in Hawai‘i alongside data on their origin, native climate types, taxonomy, and likely introduction pathway and compared rates of naturalization with socioeconomic trends. We found that the rate of total plant naturalizations has increased at a roughly constant rate during the past century without any sign of plateauing. However, this relatively steady increase is underlain by notable fluctuations in naturalization rates for different introduction pathways, with ornamentals increasing recently, while agriculture-related plants have decreased. Furthermore, this trend mirrors a shift from an agriculture-dominated economy to a tourism-based one associated with increases in both resident and tourist populations as well as general economic well-being. We further found that the average naturalized species spreads at a rate of 1.86 islands per decade, eventually occupying most major islands in the archipelago, and the rate of spread appears to be increasing since Hawai‘i’s economic shift. Our findings also emphasize the diversity of Hawai‘i’s nonnative flora, which originates from a variety of climates, continents, and taxonomic groups. We demonstrated that many nonnative species have native ranges that include temperate climates, which is important, because these climates typically co-occur with higher-elevation, remnant patches of native-dominated ecosystems in Hawai‘i. This study reveals trends that may help predict a species’ ability to naturalize and spread within and between islands, and we discuss management implications that may be extended to other regions.

We monitored colonization, spread, and growth of an exotic Old World climbing fern on tree islands in the interior marsh of Arthur R. Marshall Loxahatchee National Wildlife Refuge, Florida to investigate linkages between its colonization and growth and environmental factors. Number of the patches continuously increased over a 2-yr monitoring period, but mean patch area and height did not increase. Lower water depth was associated with larger number of patches whereas higher water depth was associated with higher mean patch height. Patch occurrence probability at each 3 m (9.8 ft) grid within tree islands also increased and indicated that patches spread from outer areas to interiors of tree islands over time. Patch occurrence probability was lower in sawgrass-dominated locations, which typically occur at the margin of tree islands, compared to locations dominated by woody plants. Patch occurrence probability was higher on west sides of tree islands corresponding to the side of the islands most impacted by a recent major hurricane. This study revealed that colonization and growth of Old World climbing fern are characterized by several spatial and temporal factors. A detection protocol using ground surveys that focus on the edges of tree islands could be an efficient way to identify early infestations on tree islands in the Refuge. Such a protocol also might be useful to identify new infestations on tree islands in other areas of the Everglades.

Black henbane is a poisonous, invasive plant in the family Solanaceae, and is typically associated with highly disturbed environments, such as pipelines, roadsides, and mammalian burrows. Often, such disturbances require reseeding for successful restoration; thus, the potential exists for competition between henbane and perennial grasses commonly used in restoration projects. These competitive interactions have not, to our knowledge, been evaluated. We conducted a greenhouse study to compare the response of henbane when grown alone and in combination with three common, cool season, perennial, northern mixed prairie grass species. We examined both seedling and mature grass response to the presence or absence of henbane and the response of henbane to the grasses. Using the relative neighbor-effect index, black henbane was found to be a very poor competitor with mature grasses and two out of three seedling grasses tested. All measures of henbane growth were significantly lower among plants grown with a mature grass pot companion. Total biomass of henbane was up to 99% lower when grown with mature grasses. Mature grasses were not negatively affected when grown in combination with henbane. Western wheatgrass (Pascopyrum smithii) was the only seedling grass that was competitive with henbane but was also the only seedling grass negatively affected by henbane in both biomass and tiller production. These experiments suggest that henbane is not well suited for invasion of mature grass stands but may negatively influence some perennial grass seedlings in restoration situations.

Bridal creeper has become a serious environmental weed in southern Australia. Historically the invaded areas had low soil nutrient levels. However, our field surveys indicate that soils in bridal creeper–invaded areas have higher phosphorus and iron levels than soils in nearby native reference areas regardless of the proximity to agriculture or other disturbances. A glasshouse experiment was undertaken to determine the influence of increased nutrients on plants that co-occur with bridal creeper in order to (1) assess the impact of changed soil conditions and (2) predict the response of dominant species following the biological control of bridal creeper. The relative growth rate (RGR) of bridal creeper, two native shrubs (narrow-leaved thomasia [Thomasia angustifolia] and bluebell creeper [Billardiera heterophylla]), and an invasive exotic grass (annual veldt grass [Ehrharta longiflora]) were determined in three soil types: soil collected within a bridal creeper stand, soil collected from a nearby reference area, and a potting mix with nutrient levels higher than that recorded in the field. The plant species were chosen due to their association with bridal creeper. For example, the native species narrow-leaved thomasia was identified in a previous survey as the most abundant shrub at the invaded site where the soil was collected. The two other species, bluebell creeper and annual veldt grass, were identified from a previous seedbank trial as being abundant (in the seedbank) and able to readily germinate in invaded areas. When grown in either the bridal creeper–invaded soil or reference soil, bluebell creeper had significantly lower RGRs than narrow-leaved thomasia and annual veldt grass. However, as all these species showed increases in RGRs between reference soil and bridal creeper soil, this study indicates that for at least these three species the impact of increased nutrients may not be a barrier to the recovery of invaded areas following the control of bridal creeper.

Hyparrhenia cymbaria (boat thatching grass, ipopo grass) and Hyparrhenia variabilis (no common name), robust African savanna grasses with complex taxonomies, have not yet been reported for the Americas. Large populations were found in central Jalisco, northeastern Michoacán, and Morelos, Mexico. The species grow in maize and sorghum fields as well as on roadsides and in old fields, but always in association with present or past sorghum cultivation; this suggests introduction through contaminated seed material from Africa. Because of the size and density of the populations, and their native ecology, they are both agricultural pests as well as a potentially dangerous invaders for the American (sub)tropical grasslands and native scrublands, including the southern United States. The invasion underlines the importance of effective phytosanitary controls of the seed supply.

To investigate the relative importance of long-distance dispersal vs. diffusion in the invasion of a nonnative plant, we used age structure to infer the contribution to recruitment of external propagule rain vs. within-population reproduction. We quantified the age structure of 14 populations of Amur honeysuckle in a landscape where it recently invaded, in Darke County, OH. We sampled the largest honeysuckle individuals in each population (woodlots), and aged these by counting annual rings in stem cross sections. Individuals in the oldest four 1-yr age classes are assumed to be from external recruitment, given the minimum age at which shrubs reproduce. We used these recruitment rates to model external recruitment over the next 5 yr and used observed age structures to estimate total recruitment. We used the difference between total and external recruitment to infer the rate of internal recruitment. Our findings indicate that recruitment from within the population is of about the same magnitude as immigration in the fifth to seventh year after population establishment, but by years 8 to 9 internal recruitment dominates. At the landscape scale, the temporal-spatial pattern of population establishment supports a stratified dispersal model, with the earliest populations establishing in widely spaced woodlots, about 4 km from existing populations, and these serving as “nascent foci” for diffusion to nearby woodlots. Understanding the relative importance of long-distance dispersal vs. diffusion will inform management, e.g., whether it is more effective to scout for isolated shrubs or remove reproducing shrubs at the edge of invaded areas.

Nonnative M. vimineum has been expanding rapidly in the eastern United States, where it can negatively affect plant communities. Locally, the species is assumed to spread from roadsides into nearby forests, where it can form dense populations after disturbances, especially in light gaps. Using microsatellite markers, we quantified patterns of genetic variation and structure among populations at nine sites in West Virginia. We then examined patterns of local dispersal within each population, focusing on subpopulations along the roadside, those coalescing nearby along the forest edge, and subpopulations in the interior forest. We found that levels of genetic variation of M. vimineum were relatively low overall across populations but with genetic structure present among populations (Fst = 0.60). Within populations, subpopulations along the roadside were genetically variable, containing 4 to 22 unique, multilocus genotypes. Many of these genotypes were also identified in the adjacent forest, consistent with local, diffusive spread from the roadway. However, several genotypes in the interior forest were unique to the population, indicating that dispersal from other sites may also occur. Overall, it appears that genetic diversity and structure in M. vimineum reflects a variety of processes, including localized dispersal and long-distance migration.

Fire is often used in northern grasslands to control invasive grass species but has unknown effects on Tamarix spp., more recent invaders. Temperature (using an oven as a fire surrogate) and duration combinations that would be most lethal to Tamarix seeds and seedlings were determined. Tamarix seeds were sown in soil-lined dishes, water added to saturation, and seedlings grown for 1 to 5 d. Seeds were also placed in water-saturated or dry soil just before temperature exposure (79 to 204 C [175 to 400 F]) by duration (1 to 5 min) treatments. After treatment, soil water loss was measured by weight difference, and surviving seedlings were counted for 6 d. Tamarix seedling establishment and survival decreased with increasing temperature and duration. The 5-d-old seedlings were the most affected. No 5-d-old seedlings survived 1- and 2-min exposures to 204 C, whereas 1-d-old seedlings had greater than 25% survival. If soils were saturated, two to four times more seedlings established following seed exposure to 177 and 204 C. Longer durations at lower temperatures were required to reduce Tamarix survival. Increasing duration from 2 to 5 min at 121 C decreased 5-d-old seedling survival from more than 80% to less than 10% and eliminated those seedlings at 149 C. Five minutes at 149 C decreased dry-soil seed viability to about 15%, whereas germination on saturated soils remained high (∼75%). No seeds survived the exposure to 177 and 204 C. Soil moisture loss values associated with 90% mortality of 5- and 1-d-old seedlings were 1.7 and 2.2%, respectively. On saturated soils, 90% of seeds died with 2.5% water loss. Under suitable conditions, fire can decrease Tamarix seedling survival. Fire may be useful for controlling Tamarix seedlings in northern grasslands and should be considered for management of new invasions.

To better understand the response of Ipomoea cairica (Cairo morningglory) to herbivory, the compensatory growth and photosynthetic characteristics of plants were measured after simulated herbivory by leaf trimming at four intensities: 25, 50, 75, and 100% removal, starting from the apex. Defoliation at 25% had no significant influence on plant biomass, but the total biomass (−19 to −66%) and root biomass (−31 to −75%) of the plants decreased significantly when defoliation intensity was ≥ 50% (P < 0.05). Photosynthetic rates (Pn) increased with defoliation intensity (P < 0.01), and Pn values in the defoliated plants were 10 to 72% greater than those in the control plants, a relationship that could be attributed to a decrease in stomatal limitation (−11 to −34%) and the increase in rubisco content (9 to 18%) as well as higher photosynthetic efficiency and less light energy dissipated as heat. At defoliation intensities up to 50%, plants needed more energy to compensate photosynthetically, which could influence the plant photosynthetic characteristics as well as the allocation of assimilates, resulting in less root development. Since the spread of I. cairica depends primarily on clonal growth, smaller roots could limit uptake of nutrients from the soil. These direct and indirect effects indicate that leaf-feeding herbivores may have potential for biological control of I. cairica but to have any effect the herbivores would need to consume ≥ 50% of the leaf biomass.

Mile-a-minute weed or devil's tearthumb (Polygonum perfoliatum, syn. = Persicaria perfoliata) is an invasive annual vine in the Mid-Atlantic and Northeastern United States that reproduces solely through seeds. Our study aimed to identify how mile-a-minute seed viability is affected by time of year and the maturity of the fruit surrounding the achene. Full-sized immature (green) and mature (blue) fruits were collected from five field sites every 2 wk over a 3 mo period, and seed viability was assessed using a triphenyl tetrazolium chloride (TZ) assay. At the onset of seed production in mid-August, 35% of seeds from immature fruits were viable. This percentage increased steadily, peaking at 84% in late September before declining at some sites around the time of the first frost. In contrast nearly all seeds with mature fruits (96%) were viable at all collection dates. Thus land managers who apply physical or chemical control methods for mile-a-minute weed should do so before the onset of any seed production and not simply before fruit maturation. If it is necessary to apply control methods after fruit set, it should be done as early in the season as possible.

There are limited educational opportunities regarding aquatic invasive species (AIS) management that target laypersons. This is a significant gap, particularly as nonprofessionals are often tasked with making decisions about whether and how to pursue AIS control efforts, for example, through their roles in community lake associations. Thus, there is a need for educational programs to help consumers of AIS management services, “do-it-yourself” lakeshore homeowners, and other engaged nonprofessionals gain a stronger foundation in the science and practice of AIS management. We helped fill this unmet need through development of a new online course, AIS Management 101, that targets lakeshore property owners, lake association members, and other nonprofessionals engaged in AIS decision making, seeking to make them better-informed consumers. The course covers concepts ranging from basic invasive species biology to pesticide science, treatment evaluation, regulations and permitting, and nonchemical management tools. Participants in the course demonstrated significant knowledge gains through check-in and check-out knowledge assessments. Course participants also reported greater understanding of key issues pertaining to AIS management and application of this improved knowledge to actual management decisions following completion of the course. While this program focuses on management of aquatic invasive species, similar approaches could be applied to lay audiences engaged in management of terrestrial invasive species or other natural resource issues.

Annual bromes (downy brome and Japanese brome) have been shown to decrease perennial grass forage production and alter ecosystem functions in northern Great Plains rangelands. Large-scale chemical control might be a method for increasing rangeland forage production. Although fall application has been shown to be the most effective and least likely to impact co-occurring native species, spring germination of downy brome may reduce the efficacy of fall-only herbicide application. We assessed the impact of a low glyphosate dose rate (210 g ha−1) applied to rangelands in fall or in fall and spring on nontarget species and on annual brome abundance at two sites in eastern Montana over 2 yr. We tested the following hypotheses: (1) nontarget effects are greater with spring herbicide application, (2) fall and spring herbicide application are necessary for effective downy brome control, and (3) fall herbicide application is sufficient to control Japanese brome. Few nontarget effects occurred; two dicotyledonous species exhibited small increases in response to herbicide. We found that that a single fall application reduced downy brome cover and seed bank density, but after the second fall application in the following year, downy brome did not continue to show a response to herbicide. After 2 yr of fall herbicide application, Japanese brome had denser seed banks in plots where herbicide had been applied. Blanket glyphosate application on rangelands is an unreliable method for controlling annual brome invasions in the northern Great Plains.

Porcelain berry and bushkiller are confamilial, exotic, perennial vines in the Vitaceae family that are considered nuisance/invasive weeds of natural and riparian areas in the eastern United States. To better understand the competitive abilities of these aggressive weeds, greenhouse competition experiments were conducted on cuttings of porcelain berry, bushkiller, and Virginia-creeper, a native member of the Vitaceae family. Plants grown singly or in combination were monitored for stem growth and biomass production. In this research, porcelain berry and Virginia-creeper exhibited similar rates of stem growth, whereas bushkiller grew taller and faster than either of the other species. Porcelain berry stem growth was reduced in competition with bushkiller. All three species exhibited reduced stem biomass when grown with both other species. Root biomass of porcelain berry and Virginia-creeper were not affected by competition, but bushkiller, which produced the heaviest roots, exhibited reduced root biomass when grown with both other species. Porcelain berry root length was reduced by competition with both other species, but neither Virginia-creeper nor bushkiller root lengths were affected by competition. These results indicate that bushkiller is likely the strongest competitor of the three species studied. In these experiments, porcelain berry was less aggressive and vigorous than bushkiller but was similar to Virginia-creeper.

Jamaican nightshade is a prickly, perennial, invasive shrub in central and southern peninsular Florida. It was first seen in Florida in 1930 near St. Cloud, and has since been reported at several other locations in the state. Jamaican nightshade is primarily found in wooded habitats, where it can quickly become dominant in the understory, but it also occasionally grows in isolated patches in the open. Although the distribution of Jamaican nightshade does not appear to be rapidly expanding in Florida, land mangers should be made aware of the potential of this weed to establish at new sites, and initiate control efforts during the early stages of colonization at newly invaded sites.

To successfully reduce overall invasive plant cover over time, an effective treatment plan must be established such that mortality exceeds new colonization and resprouting growth rates. However, few evaluations of the effects of long-term, consistent treatment at different intervals exist. We report the effects of treatment intensity on Old World climbing fern [Lygodium microphyllum (Cav.) R. Br.], Brazilian pepper (Schinus terebinthifolia Raddi), and punktree [Melaleuca quinquenervia (Cav.) S. F. Blake] as part of a large restoration project that has been underway for 6 yr in Telegraph Swamp at Babcock Ranch Preserve, a 27,520-hectare (68,000-acre) conservation area in Florida, USA. We found that at the end of the 6-yr period, for all three species, average live cover did not exceed 5% across all transects. In addition, dead foliar cover was higher than live cover for all three invasive plants, indicating progress toward restoration goals. We also found that percent live cover of L. microphyllum was significantly reduced only after four or more treatments were applied during the 6-yr period, as opposed to when three or fewer treatments were applied. Reductions in percent cover of live foliage were apparent only when the treatments were applied more often than biennially, as opposed to less often than biennially. Additionally, we found higher L. microphyllum cover in clear-cut and replanted cypress stands than in natural stands. Based on these findings, we conclude that treatments applied four or more times, or more often than biennially, were more effective at significantly reducing advanced invasions of L. microphyllum, S. terebinthifolia, and M. quinquenervia, especially where previous management activities or their effects may have increased the cover of invasive plants.

Black henbane can be either annual or biennial. We investigated which life cycle is found in four introduced western North American populations. Plants were grown in a greenhouse common garden until half were vernalized by exposure to natural winter temperatures, while the other half remained in the greenhouse above 20 C, with 16 h of light and 8 h of dark. In total the plants were monitored 313 d after germination. We measured whether plants bolted, the time it took for bolting to commence, and the size at bolting. All vernalized plants bolted after 117 d of active growth (within 26 d of the end of the vernalization treatment), whereas only 26% of the nonvernalized plants bolted after an average of 278 d of active growth. Vernalized plants bolted at a smaller size than the nonvernalized plants that bolted (28 vs. 41 leaves on average). In the nonvernalized plants, the relationship between time to bolting and size was strong, but not so with the vernalized plants. Our results indicate that introduced black henbane plants are biennial, and that vernalization is more critical to bolting and flowering than reaching a certain size. Nonetheless, the fact that nonvernalized plants were capable of bolting if grown long enough suggests that vernalization is not the only cue that can trigger reproduction in introduced populations.